Based on some Q&A:


Global Register Allocation: This is about placing in registers values
that are used a lot in performance-critical code: local variables and
method arguments if possible will be placed in the callee-saved
registers that are returned by th arch-specific code in the function:
mono_arch_get_global_int_regs().


Stack Unwinding: is the process that happens during exception
handling: when an exception is thrown in a called method and caught in
a caller method, me need to put the processor registers in the state
they were in the caller, at the point where the catch handler can run.

This happens in the mono_handle_exception_internal() and
mono_arch_find_jit_info(): see the other architectures implementations
for ideas: they basically need to know how big was the stack allocated
in each call frame and they need to restore the callee-save registers
that were saved in the stack in the prolog in the called functions (
during stack unwindong the epilog of a method is not executed and the
register restoration needs to be done manually in the above
functions).